This invention relates to a process for granulating an azobisamidine salt used as a polymerization initiator in aqueous solution polymerization and emulsion polymerization.
Azobisamidine salts exemplified typically by 2,2'-azobisisobutylamidine hydrochloride or acetate, 2,2'-azobis(N,N'-dimethyleneisobutylamidine) hydrochloride or acetate, etc., are readily soluble in water as estimated from their structures, and thus used as a polymerization initiator in aqueous solution polymerization or emulsion polymerization. That is, when they are used in the form of an acidic aqueous solution, they act as highly active water-soluble polymerization initiators. Further, when they are used as a polymerization initiator for emulsion polymerization, there is obtained a polymer having positively charged terminals. The azobisamidine salts can be used variously, for example, for polymerization of water-soluble monomers such as acrylamide, allylamine, vinylpyrrolidone, etc., production of cationic polymers, polymerization of fluorine resins, various emulsion polymerization, photopolymerization, and the like. The azobisamidine salts are usually in the form of fine powder and irritate the skin, so that they are unfavorable for handling from the viewpoint of health. But, the azobisamidine salts are highly active in aqueous solution and are easily decomposed as mentioned above, and it is well known that when they are allowed to stand in water, they deteriorate in quality with the lapse of time. Therefore, the use of water for granulation of the azobisamidine salts was not thought of, although the granulation of azobisamidine salts has long been desired. Further, since there has been found no suitable binder for the granulation, the azobisamidine salts have been used in the form of fine powders.